Step-by-step processes for planning and designing drip irrigation systems

By Lynette Petersen

Just a few years ago, irrigation professionals were questioning the use of low-volume irrigation products. Today, however, professionals are well aware that drip irrigation systems can save significant amounts of water, and still provide the irrigation necessary for healthy, beautiful plants.

Although contractors have accepted drip irrigation as a good water management practice, proper planning and design continue to raise questions. Drip irrigation systems aren’t necessarily more difficult — they’re simply different. By doing your homework and planning ahead, you can implement drip irrigation systems that use water responsibly while allowing landscapes to flourish.

Is drip irrigation right for your landscape?

Overhead, broadcast methods of irrigation are ideal for turf, which requires a uniform precipitation rate over its entire planted area. However, the use of overhead irrigation in sparsely planted, non-grass areas can waste water on unplanted ground, or, even worse, promote weed growth. These systems also lack the flexibility to deliver different amounts of water to different plants in the same planting area. According to Stan Wager, director of landscape drip and agri-products for Rain Bird Corporation, if you want to irrigate any non-turf area including flowerbeds, ground cover, street medians, vegetable gardens and hanging baskets — drip irrigation may be your most efficient option.

“Not only does drip irrigation save water, it also reduces the amount of time spent on maintenance,” said Wager. “By only watering the plants you want to grow, you can avoid providing water for unwanted weeds in open areas, reducing the need for herbicides and the time spent manually pulling weeds.”

When deciding if a drip irrigation system is appropriate for your particular application, consider the following important factors:

• Installation costs. In most cases, the cost of materials will be similar for low-volume and conventional irrigation systems. The cost of labor, however, may be less for a low-volume system, because you can often install it at or near grade — requiring less trenching.
• Size of area. Generally, non-grass planting areas of any size can use low-volume irrigation. There are, however, two considerations: plant density and maintenance. For example, a large, densely planted area with a homogeneous plant material generally requires uniform watering over a fairly consistent root depth, and can be irrigated with broadcast methods. However, the fact remains that drip irrigation can provide adequate hydration to any area, small or large.
• Possibility of vandalism. In areas where vandalism can be a problem, it is important to design a system that can be installed below grade as much as possible, with exposed components placed out of sight. Drip irrigation is an excellent choice for these types of situations.

“A properly designed drip system is much more vandal-proof than a conventional system,” Wager added. “The delivery devices can easily be masked by the plants or hidden from vandals under mulch.”

• Safety. Low-volume systems provide greater safety by reducing run-off on walks and paved areas, and overthrow into the street or pedestrian right-of-way.
• Intended use. Low-volume irrigation may be less appropriate for sites with heavy traffic, because the exposed tubing can be damaged. Frequent soil cultivation may also damage low-volume tubing.

Drip system design

Although installation and maintenance of a drip system is no more labor-intensive or complex than that of a traditional system, designing a drip system for maximum water distribution efficiency does require forethought. Drip irrigation designs can only truly optimize the application of water if water waste below the plant root zone is taken into consideration. The best design for a drip irrigation system is one that minimizes water waste below the root zone and strives to apply the precise amount of water required by each individual plant or group of plants in a landscape.

“A drip irrigation system can save up to 50 percent of the water used by a conventional irrigation system,” said Wager. “However, this type of performance can only be achieved with careful planning and proper design.”

Some steps to design an efficient low-volume irrigation system are as follows:

1. Gather accurate site data. Although accurate data is important to any irrigation design, it is even more important with low-volume irrigation, because water is distributed in more precise amounts. Site data encompasses information such as water source(s), soil type, climate and hydrozones. It is also important to note whether areas are densely planted or sparsely planted different planting schemes dictate different design approaches and related drip products.
2. Determine plant water requirements. Calculate the precise amount of water needed by each type of plant within the irrigation site. By doing so, you’ll be able to figure out the most effective irrigation methods and types of emitters required for different groups of plantings. To calculate each plant’s water requirements, you’ll need to take into account several factors, including species, climate and planting density.
3. Irrigate your “base plant.” Base plants are those plants within the irrigation area that require the least water. Irrigate this plant to determine how long it takes to provide adequate hydration. The remainder of your system will be designed to deliver the required amount of water to all other plants in the same amount of time it takes to water the base plant. Your irrigation product manufacturer can provide advice about the best emission devices and appropriate spacing, pressure, flow rate and filters for your application.
4. Calculate system run time. As stated in Step 3, system run time is dictated by the irrigation needs of the base plant, meaning that flow rates to other plants must be adjusted for adequate hydration during that same amount of time. You’ll also need to determine your maximum system run time (the length of time your system can run before you begin to waste water.) This time depends on the flow rates of your emitters and the allowable depletion of your soil. From there, you can also determine your irrigation interval how often you’ll run your system.
5. Irrigate “non-base plants.” To irrigate non-base plants, you will need to calculate the number of emission devices required for each plant by dividing the daily water requirement for each remaining plant by the system run time you calculated in Step 4. This tells you the minimum flow rate required for each plant and allows you to select the emission devices necessary to meet or exceed that flow rate.
6. Lay out the system. Once you’ve determined the type, number and spacing of emission devices required for each plant or group of plants, simply determine the most cost-effective layout to connect the various emission devices to the water source via tubing or PVC pipe.
7. Calculate system hydraulics. This step is imperative to ensure that there is sufficient flow and water pressure to irrigate all parts of the landscape. These factors are influenced by changes in elevation and friction between water and system components. Calculating your system hydraulics enables you to determine the maximum allowable pressure loss, which, in turn, tells you the maximum length of your dripline laterals.

Landscape and irrigation designers can use these steps to design systems based not only on the size of a planted area, but on a plant’s root depth, soil type, water requirement and density of planting for the greatest efficiency possible. Although the design process requires time and precision, the end result will be worth it.

Drip irrigation systems — not difficult, just different

Water is the world’s most precious resource, and as time passes, it becomes increasingly important for all of us to use water responsibly in our daily lives. Drought conditions and water restrictions throughout much of the country have caused the concept of drip irrigation to become more and more popular. These systems are no more difficult to design and install than conventional irrigation systems, and their outstanding flexibility and top-notch results make them well worth any extra effort. Drip irrigation has truly established itself as cost-effective way for proactive irrigation contractors to promote intelligent water usage and differentiate their businesses.

Lynette Petersen is public relations counsel for Swanson Russell Associates.

Article provided by Rain Bird Corporation. The step-by-step design process detailed above is based on actual research performed by Rain Bird Corporation. For more in-depth information about each of these steps, as well as worksheets and formulas to assist with the design of your drip irrigation system, download Rain Bird’s Low-Volume Landscape Irrigation Design Manual at http://www.rainbird.com/pdf/drip/LowVolumeGuide.pdf.